Soda-lime-silica glass is mostly widely used, mainly for production of flat glass and various glass products. The output of flat glass in China is about 0.74 billion weight case, in the order of 37 million tons. It can be determined according to a Na2O-CaO-SiO2 system phase diagram that the composition range that can form glass is, in % by weight, 12˜18wt % of Na2O, 6˜16wt % of CaO, and 68˜82wt % of SiO2. The composition of common glass is, in % by weight, 12˜15wt % of Na2O, 8˜13wt % of CaO, and 69˜73wt % of SiO2. In such glass of ternary system, two types of composition of precipitated crystal can be easily formed, i.e. devitrite (Na2O.CaO.SiO2) and wollastonite (CaO.SiO2). It was found in production practice that the introduction of MgO (which may partially replace CaO) and Al2O3 not only improves crystallizability of the glass, but also increases thermal stability and chemical stability. Moreover, partial replacement of Na2O with K2O has “double alkali effect”, and can improve chemical stability and luster of the glass. Except for high-alumina glass, the amount of Al2O3 is generally not exceeding 10 wt %, usually between 0.5 and 3 wt %,
As is well known, coal ash is a common high-silicon powdery industrial waste, which is discharged from chimneys and furnace bottoms of coal-fired power plants after finely ground coal powder was burnt in the furnaces. China is rich in coal resources. In recent years, the annual consumption of thermal coal has reached above 1.7 billion tons, while the annual output of coal ash has exceeded 0.4 billion tons. In the previous studies, to make maximum use of respective components of coal ash, coal ash was usually used directly as raw material for production of foam glass and microcrystal glass (Xiaoping FENG: Application of Coal ash in Glass Industry, Coal Ash, 2004, 3, 24-26). However, a modest usage amount of these two glasses restricts a further development of glass manufactured with coal ash. Due to scarcity of bauxite resources in China, and the amount of aluminum oxide generally takes up 16.5 to 35.4 wt % of coal ash, or up to above 50 wt %, thus, the research and development of the process for extracting aluminum from coal ash has been attached great importance, mainly including the acid process, alkali process, acid and alkali combination method, ammonium sulfate process, etc., among which, the soda lime sintering process based on pre-desiliconization can produce byproducts such as white carbon black, dicalcium silicate, calcium silicate, which is conducive to improving economical efficiency of extracting aluminum from coal ash.
The method for preparing a soda-lime-silica glass basic formulation, the method for producing soda-lime-silica glass, as well as the process of extracting aluminum from coal ash for co-production of glass as presented by this invention break through the routine process for manufacturing glass, by utilizing silicon-containing powdery industrial waste such as coal ash, and using silicon dioxide obtained from alkali dissolution and desiliconization of an alkaline solution and calcium carbonate resulting from caustification as principal raw materials, which not only produce common glass which is in great demand, but also produce high value-added ultra-white glass. By treating coal ash with an alkaline solution, the present invention enables the glass phase with higher reactivity, which is mainly composed of silicon dioxide, to react with a sodium hydroxide solution, to give a pre-desiliconization mother liquor mainly consisting of sodium silicate, and a few amount of sodium aluminate. After carbonation decomposition, the pre-desiliconization mother liquor is separated to obtain a silicic acid precipitate and a sodium carbonate solution. The silicic acid precipitate is dried to obtain silicon dioxide, which may serve as silicon source and aluminum source for production of soda-lime-silica glass. Moreover, lime milk is added into a sodium carbonate solution for causticization to obtain a calcium carbonate precipitate and a caustic alkali solution. The dried calcium carbonate precipitate can serve as calcium source for production of soda-lime-silica glass. Sodium carbonate and sodium hydroxide are entrained in silicon dioxide and calcium carbonate, and can serve as part of the sodium source for production of soda-lime-silica glass.
Compared to the traditional process for producing soda-lime-silica glass, the process for producing soda lime glass presented by this invention integrates and optimizes a process of extracting aluminum from the coal ash, realizes comprehensive use of solid waste, has a high material and energy utilization rate and a good product quality, and can greatly improve economical efficiency of extracting aluminum from coal ash.